This invention relates to a digital computer system that has an expandable processor section. More particularly, the invention provides a computer system that has a system bus interconnecting a processor section, a memory section and an input-output section, and in which the processor section can have a variable compliment of highly autonomous processor units. A computer system according to the invention can thus have, by way of example, one processor unit, two processor units, five processor units or eight or more processor units--to provide progressively greater or lesser processing capacity--without any change by the operator of either software or hardware, other than connecting the desired number of processor units to the system.
The invention further provides a processor unit for substantially autonomous operation in a computer system of the above character with substantially any number of other like processor units.
The invention is particularly applicable to a computer system in which the processor section is highly or even entirely distributed, in that it consists of one or more processor units and has little or no centralized control or supervisory logic or software imposed over the processor units. One example of such a computer system is a fault tolerant computer system that has a selected redundancy of operational elements organized in a manner to provide substantially continuous operation even in the event of one or more faults or failures.
Stratus Computer, Inc., the assignee of this application, is one manufacturer of such computer systems and has marketed such products under the designations FT200, XA400, and XA600. U.S. Pat. No. 4,453,215 assigned to that company describes one fault tolerant computer system of the foregoing type with which the present invention is advantageously practice.
The expansion, and conversely contraction, of a computer processor section by the addition or removal of processor units, to meet changing demands for processing capacity, can be effected relatively easily in a computer system that has a centralized command element that assigns tasks among the processor units. However, such centralized organization often is undesirable. Instead, a decentralized organization is preferred, with autonomous processor units.
Accordingly, it is an object of this invention to provide an improved method and apparatus for the expansion of a computer processor section.
A further object is to provide an improved method and apparatus for changing the number of substantially autonomous processor units that constitute a computer system processor section.
A more particular object is to provide a digital computer system having a processor section with substantially autonomous processor units and which is readily expandable. A further object is to provide a computer system of the above character in which the number of processor units can be changed with minimal operator action and with minimal change in system operating programs and procedures.
Yet another object of the invention is to provide a central processor unit for connection with one or more other similar processor units in a computer system processor section and which includes substantially autonomous means for effecting the distribution of processor tasks, substantially equally or selectively otherwise, among whatever other processor units are in the processor section of the data processing system.
Other objects of the invention will in part be obvious and in part appear hereinafter.